Heretofore, a phosphorus-containing compound has been generally used both an anti-wear agent and an antioxidant to be used in engine oils, diesel oils, or the like for internal combustion engines. A large number of manufacturers have dealt with the need for such anti-wear agent and antioxidant by combining an organic zinc compound or an organic molybdenum compound with an additive (for example, Patent Documents 1 to 3).
Patent Document 1 discloses a lubricating oil composition for an internal combustion engine characterized by containing, with respect to a lubricating oil base oil (a mineral oil or a synthetic oil), 0.01 to 0.2 wt % in terms of a molybdenum (Mo) amount of sulfurized oxymolybdenum dithiocarbamate, 0.01 to 0.2 wt % in terms of a phosphorus (P) amount of zinc dithiophosphate, and 0.2 to 5 wt % of a phenol-based antioxidant having an ester group.
In addition, Patent Document 2 discloses a diesel engine oil for an engine with an exhaust gas recirculation apparatus, the oil being characterized in that a lubricating oil base oil (a mineral oil or a synthetic oil) is blended with 5.8 to 8.3 mass % of a calcium alkyl salicylate (calcium (Ca) content: 6.0 mass %) having a total basic number (TBN) of 165 mgKOH/g as a detergent, 0.09 to 0.13 mass % in terms of zinc (Zn) of a primary alkyl-type zinc dithiophosphate as an antioxidant-cum-anti-wear agent, and 0.02 to 0.04 mass % in terms of molybdenum (Mo) of an oil-soluble oxymolybdenum dialkyl dithiophosphate as a friction modifier-cum-anti-wear agent.
Further, Patent Document 3 discloses a lubricating oil composition for an internal combustion engine characterized in that a base oil formed of a mineral oil and/or a synthetic oil is blended with (A) 0.08 to 0.40 mass % in terms of a nitrogen element of a succinimide-based ashless dispersant, (B) 0.06 to 0.22 mass % in terms of a metal element of a metal-based detergent, (C) 0.04 to 0.08 mass % in terms of a phosphorus element of a secondary alkyl zinc dithiophosphate, and (D) 0.01 to 0.04 mass % in terms of a phosphorus element of a phosphorus-containing ashless anti-wear agent, and that the content of sulfated ash derived from a metal element in the composition is 0.3 to 1.0 mass %. The document also discloses a lubricating oil composition for an internal combustion engine characterized by being blended with 0.01 to 0.04 mass % in terms of a phosphorus element of a phosphorus-containing ashless anti-wear agent, and characterized in that the content of sulfated ash derived from a metal element in the composition is 0.3 to 1.0 mass %.